Focus on Energy: Window Worries

A glass scientist explained to me
once that float glass is actually a
"supercooled liquid" that never
completely solidifies. "The glass in
your windows is slowly flowing
away," he said. "In fact, if you
measure the glass in a 100-yearold
window, you'll see that it is
thickest near the bottom because
it is flowing down."
Few people would lose sleep over
the fact that their window glass
may melt away in a few hundred
years. There is some concern,
however, over the degradation
and disappearance of newer elements
in windows, namely the
low-emissivity coating and argon
gas filling which are responsible
for the insulating power of highperformance
glazings.
How long does that low-e coating
last? Is there a way to tell that
it